Objectives: 1. Studies of factors affecting distribution of bilirubin in red cells and skin of jaundiced infants are in progress. The major aim is to develop a direct assay of risk from brain damage caused by bilirubin, and to determine the rate-limiting steps in the degradation of bilirubin by phototherapy. 2. Studies of enzyme defects in the urea cycle of children with Reye's syndrome will be expanded. The object of these assays will be to determine whether these defects are inherited or acquired, and whether treatment with specific substrates may ameliorate the condition. 3. Serum tripeptides which have been shown to influence growth in liver cell cultures appear to have insulin-like properties. The mechanisms of these biological effects, and their relationship to each other will be investigated in cell cultures of normal and malignant liver cells.